py/qstr: Add support for MICROPY_QSTR_BYTES_IN_HASH=0.

This disables using qstr hashes altogether, which saves RAM and flash
(two bytes per interned string on a typical build) as well as code size.
On PYBV11 this is worth over 3k flash.

qstr comparison will now be done just by length then data. This affects
qstr_find_strn although this has a negligible performance impact as, for a
given comparison, the length and first character will ~usually be
different anyway.

String hashing (e.g. builtin `hash()` and map.c) now need to compute the
hash dynamically, and for the map case this does come at a performance
cost.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

1 files changed, 12 insertions, 15 deletions

diff --git a/tools/mpy-tool.py b/tools/mpy-tool.py
index 8d86c1017..519462ec8 100755
--- a/tools/mpy-tool.py
+++ b/tools/mpy-tool.py
@@ -1473,21 +1473,20 @@ def freeze_mpy(firmware_qstr_idents, compiled_modules):
     raw_code_count = 0
     raw_code_content = 0
 
-    print()
-    print("const qstr_hash_t mp_qstr_frozen_const_hashes[] = {")
-    qstr_size = {"metadata": 0, "data": 0}
-    for _, _, _, qbytes in new:
-        qhash = qstrutil.compute_hash(qbytes, config.MICROPY_QSTR_BYTES_IN_HASH)
-        print("    %d," % qhash)
-    print("};")
+    if config.MICROPY_QSTR_BYTES_IN_HASH:
+        print()
+        print("const qstr_hash_t mp_qstr_frozen_const_hashes[] = {")
+        for _, _, _, qbytes in new:
+            qhash = qstrutil.compute_hash(qbytes, config.MICROPY_QSTR_BYTES_IN_HASH)
+            print("    %d," % qhash)
+            qstr_content += config.MICROPY_QSTR_BYTES_IN_HASH
+        print("};")
     print()
     print("const qstr_len_t mp_qstr_frozen_const_lengths[] = {")
     for _, _, _, qbytes in new:
         print("    %d," % len(qbytes))
-        qstr_size["metadata"] += (
-            config.MICROPY_QSTR_BYTES_IN_LEN + config.MICROPY_QSTR_BYTES_IN_HASH
-        )
-        qstr_size["data"] += len(qbytes)
+        qstr_content += config.MICROPY_QSTR_BYTES_IN_LEN
+        qstr_content += len(qbytes) + 1  # include NUL
     print("};")
     print()
     print("extern const qstr_pool_t mp_qstr_const_pool;")
@@ -1497,14 +1496,12 @@ def freeze_mpy(firmware_qstr_idents, compiled_modules):
     print("    true, // is_sorted")
     print("    %u, // allocated entries" % qstr_pool_alloc)
     print("    %u, // used entries" % len(new))
-    print("    (qstr_hash_t *)mp_qstr_frozen_const_hashes,")
+    if config.MICROPY_QSTR_BYTES_IN_HASH:
+        print("    (qstr_hash_t *)mp_qstr_frozen_const_hashes,")
     print("    (qstr_len_t *)mp_qstr_frozen_const_lengths,")
     print("    {")
     for _, _, qstr, qbytes in new:
         print('        "%s",' % qstrutil.escape_bytes(qstr, qbytes))
-        qstr_content += (
-            config.MICROPY_QSTR_BYTES_IN_LEN + config.MICROPY_QSTR_BYTES_IN_HASH + len(qbytes) + 1
-        )
     print("    },")
     print("};")